Browsing by Author "Srivastava, R"

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    Experimental (FT-IR, FT-Raman, UV and NMR) and quantum chemical studies on molecular structure, spectroscopic analysis, NLO, NBO and reactivity descriptors of 3,5-Difluoroaniline
    Pathak, SK; Srivastava, R; Sachan, AK; Prasad, O; Sinha, L; Asiri, AM; Karabacak, M
    Comprehensive investigation of geometrical and electronic structure in ground as well as the first excited state of 3,5-Difluoroaniline (C6H5NF2) was carried out. The experimentally observed spectral data (FT-TR and FT-Raman) of the title compound was compared with the spectral data obtained by DFT/B3LYP method using 6-311++G(d,p) basis set. The molecular properties like dipole moment, polarizability, first static hyperpolarizability, molecular electrostatic potential surface (MEPs), and contour map were calculated to get a better insight of the properties of the title molecule. Natural bond orbital (NBO) analysis was applied to study stability of the molecule arising from charge delocalization. UV-Vis spectrum of the title compound was also recorded and the electronic properties, such as Frontier orbitals and band gap energies were measured by TD-DFT approach. Total and partial density of state (TDOS and PDOS) and also overlap population density of state (OPDOS) diagrams analysis were presented. Global and local reactivity descriptors were computed to predict reactivity and reactive sites on the molecule. H-1 and C-13 NMR spectra by using gauge including atomic orbital (GIAO) method of studied compound were compared with experimental data obtained. Moreover, the thermodynamic properties were evaluated. (C) 2014 Elsevier B.V. All rights reserved.
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    A combined experimental and theoretical DFT (B3LYP, CAM-B3LYP and M06-2X) study on electronic structure, hydrogen bonding, solvent effects and spectral features of methyl 1H-indol-5-carboxylate
    Srivastava, R; Al-Omary, FAM; El-Emam, AA; Pathak, SK; Karabacak, M; Narayan, V; Chand, S; Prasad, O; Sinha, L
    Investigation of ground state geometry, molecular properties and electronic structure of methyl 1H-indol-5-carboxylate has been reported for the first time using the implements of density functional theory. The two possible conformers of the title compound were first optimized at B3LYP/6-31G(d) and then further at B3LYP, M06-2X and CAM-B3LYP functionals at 6-311++G(d,p) basis set. A comprehensive vibrational analysis has been performed for both the conformers at B3LYP/6-311++G(d,p). Good agreement between theoretical spectral data with experimental spectra has been obtained. Polarizability and first static hyperpolarizability have been compared at different functionals used in the present study. To estimate the intra-molecular delocalization along with the inter-molecular interaction, the NBO analysis has been done for monomer and dimer of the title molecule. Topological parameters at the bond critical point involved in intermolecular hydrogen-bonding have also been calculated using AIM theory to assess the strength of hydrogen bonding. Effects of solvents (water, carbon tetrachloride and chloroform) on the optimized geometry and the inter-molecular hydrogen bonding have been evaluated. UV-Vis spectrum of the title compound was also recorded and electronic properties such as frontier orbitals and their corresponding energy gap have also been calculated by TD-DFT approach.
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    Spectral features, electric properties, NBO analysis and reactivity descriptors of 2-(2-Benzothiazolylthio)-Ethanol: Combined experimental and DFT studies
    Srivastava, R; Sinha, L; Karabacak, M; Prasad, O; Pathak, SK; Asiri, AM; Cinar, M
    Quantum chemical calculations of ground state energy, geometrical structure and vibrational wavenumbers, nuclear magnetic behaviors, electronic absorption spectra along with the nonlinear optical properties of 2-(2-benzothiazolylthio)-ethanol (BTZTE) were carried out using density functional (DFT/B3LYP) method with 6-311++G(d,p) as basis set. The FT-IR and FT-Raman spectra were measured in the condensed state. The fundamental vibrational wavenumbers as well as their intensities were calculated, and a good correlation between experimental and scaled calculated wavenumbers was accomplished. The electric dipole moment, polarizability and the first hyperpolarizability values of the BTZTE were calculated at the same level of theory and basis set. The results show that the BTZTE molecule possesses nonlinear optical (NLO) behavior with non-zero values. Stability of the molecule arising from hyper-conjugative interactions and charge delocalization was analyzed using natural bond orbital (NBO) analysis. UV spectrum of the studied molecule was recorded in the region 200-500 nm and the electronic properties were predicted by time-dependent DFT approach. The calculated transition energies are in good concurrency with the experimental data. H-1 nuclear magnetic resonance (NMR) chemical shifts of the title molecule were calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. The thermodynamic properties of the studied compound at different temperatures were calculated. Global and local reactivity descriptors were computed to predict reactivity and reactive sites on the molecule. (C) 2014 Elsevier B.V. All rights reserved.